Recent years have seen active development of compact and lightweight electronic devices. Liquid crystal display devices mounted in such electronic devices are required to consume less power. A drive method to reduce power consumption by the liquid crystal display device is a drive method called “pause drive” with drive periods in which scanning lines are scanned to write signal voltages and pause periods in which the writing is paused by keeping all of the scanning lines in unscanned state. In the pause drive, a scanning line driver circuit and/or a data signal line driver circuit are/is provided with no control signals and suchlike during the pause period, so that the operation of the scanning line driver circuit and/or the data signal line driver circuit can be stopped. As a result, it is possible to reduce power consumption by the liquid crystal display device. The pause drive as described above is also referred to as “low-frequency drive” or “intermittent drive”.
In a liquid crystal panel for use in the liquid crystal display device, a liquid crystal layer is provided between two electrodes. When a voltage is applied to the liquid crystal layer, the orientation direction (i.e., the longitudinal direction) of liquid crystal molecules in the liquid crystal layer changes because of dielectric anisotropy of the liquid crystal. Moreover, liquid crystals have optical anisotropy, and therefore, when the orientation direction of the liquid crystal molecules changes, the direction of polarization of light to be transmitted through the liquid crystal layer changes. Accordingly, the amount of light to be transmitted through the liquid crystal layer can be controlled in accordance with the voltage applied to the liquid crystal layer. Thus, it is possible to display an image on the liquid crystal panel with the luminance of each pixel forming portion at a desired grayscale luminance value.
However, it takes a certain period of time for the liquid crystal to respond to a change in the applied voltage. For example, in the case of a widely used TN (Twisted Nematic), IPS (In-Plane Switching), or VA (Vertically Aligned) liquid crystal display device, it might take a time period of about 50 ms until the liquid crystal responds. In addition, it is known that the response speed of the liquid crystal changes in accordance with the temperature, and the response speed decreases as the temperature lowers.
Furthermore, when the frequency of an image signal is 60 Hz, the duration of a frame period is 16.7 ms. Accordingly, if the response period of the liquid crystal becomes longer than one frame period, image lag might occur on the screen, resulting in reduced image display quality.
Therefore, to solve the above problems, for example, Japanese Laid-Open Patent Publication No. 2004-4629 discloses a liquid crystal display device in which “overshoot drive” is performed to apply a higher voltage to a liquid crystal layer than a normally applied voltage. The overshoot drive is performed using a look-up table (referred to as an “LUT” or a “table”) in which correction values are stored and correlated with combinations of grayscale values for the previous and current frames. More specifically, a correction value corresponding to a combination of grayscale values for the previous and current frames is read from the LUT and used to correct an input image signal, so that the corrected image signal is outputted. By performing overshoot drive using such a corrected image signal, it is rendered possible to increase the response speed of the liquid crystal, and hence the response speed of the liquid crystal display device.